1. Field of the Invention
The present invention relates to a cylinder operation control apparatus for an internal combustion engine, which enables a switching operation between an all-cylinder activation mode in which all cylinders of the engine are activated, and a cylinder deactivation mode in which at least a cylinder of the engine is deactivated.
2. Description of the Related Art
Among hybrid vehicles, a type of hybrid vehicle is known in which a cylinder deactivation operation is executed, for example, by controlling valve trains of the engine using hydraulic control method in order to further improve fuel economy by means of reduction in friction of the engine. In this type of hybrid vehicle, when the vehicle enters a deceleration state, a cylinder deactivation operation is executed along with a fuel cut operation so as to decrease engine friction, and as a result, the amount of regenerated electric energy is increased by an amount corresponding to the decreased engine friction, and thus fuel economy is improved (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 07-63097).
Accordingly, if an engine is employed, in which an all-cylinder deactivation operation is made possible, energy, which would have been dissipated due to engine friction during a deceleration operation, can be maximally recovered, and thus a hybrid vehicle having excellent fuel economy can be obtained.
As described above, fuel economy can be greatly improved by employing an all-cylinder deactivation operation; however, in general, some of the cylinders must remain as normally activated cylinders so as to be able to drive the vehicle upon resuming fuel supply to the activated cylinders just in case the cylinder deactivation mechanism fails. Accordingly, friction due to the normally activated cylinders remain unchanged during a deceleration operation; therefore, fuel economy is not greatly improved.